Insulation piercing electrical contact, especially for medical disposable articles such as fetal scalp electrodes

ABSTRACT

The insulation piercing electrical contact in accordance with the invention consists of a first contact element ( 20 ) for establishing an electrical contact with a second contact element ( 30 ), a contacting member ( 50 ) piercing an electrical conductor ( 60, 63 ) when the two contact elements ( 20, 30 ) are joined. The first contact element is provided with a molding ( 20 ) that encloses the electrical conductor ( 60, 63 ) at the contact side and electrically insulates it.

BACKGROUND OF THE INVENTION

The present invention relates to contact elements for establishing anelectrical contact in that, when the contact elements are joined, acontact element cuts into or pierces an electrical conductor.

Plug-type connections generally are disengageable or non-disengageableelectrical connections of one or more contacts, electrical contact beingestablished by inserting complementary contact elements, such as a plugand a socket, one into the other.

In the case of disengageable contacting a connection is regularlyestablished in that one contact element bears resiliently against theother element or is clamped onto the other element. In this respectthere are many alternatives such as, for example sockets and resilientpins, resilient sockets and pins, leaf springs on pads, shear clamps,wire clamps, pin clamps, screw-type clamps for wires or pins and so on.Plug-type connections of this kind are customarily provided for numerousinsertion and withdrawal cycles.

As opposed to the disengageable electrical connections, in the case ofnon-disengageable electrical connections an electrical contact is to beestablished that is regularly only a one-time, non-disengageableelectrical connection. Among the non-disengageable electricalconnections there are notably the piercing clamping connections where aone-time contact is established through an insulated cable by means of apiercing element. Contacting normally takes place in the directionperpendicular to the sheath of the electrical conductors.

Finally, in addition to the disengageable or non-disengageableelectrical connections in the strict sense of the word there are alsohybrid forms that are designed for more or less numerous insertion andwithdrawal cycles, for example, piercing clamping connections that areintended for a given number of insertion and withdrawal cycles. Piercingclamping connections of this kind are described inter alia inEP-A-131705 or WO 98/29031.

Nowadays a typical example of a disengageable electrical connection isencountered in the medical field for the purpose of birth monitoring,that is, for the so-called fetal galea or scalp electrodes formonitoring the fetal cardiac activity. The fetal scalp electrode is usedto record the ECG of the unborn child by means of two electrodes. At theside of the scalp electrodes there are provided two open (bared) tinnedwires for contacting two resilient jaws as counter contacts at theapparatus side. Applicant discloses fetal scalp electrodes of this kindinter alia in U.S. Pat. No. 5,423,314 or U.S. Pat. No. 3,750,650.

The fetal scalp electrode customarily is a disposable product;therefore, like other medical disposable articles it should be asinexpensive as possible. The simple bare contact wires satisfy this costrequirement.

International regulations, such as imposed by the FDA (Food and DrugAdministration) or MDD (Medical Device Directive), stipulate that theopen, electrically conductive wires of the fetal scalp electrodes mustbe replaced by an insulated plug-type connector so as to protect thepatients against incorrect contacting.

A further requirement that is imposed in particular on fetal scalpelectrodes is that the plug element should be as small as possible,because must be easy to pull this element through an inner tube of anintroduction instrument in the known embodiments.

A plug-type connection of this kind for fetal scalp electrodes thatnotably satisfies said safety regulations is known from EP-A-484107.According to that plug-type connection system the two wires areconnected to insulated sockets (in conformity with the known jack plugconnection), said sockets subsequently being placed on pins. Thisarrangement, however, has the drawback that, because of the necessarylimitation of the dimensions of the plug element, its manufacture isintricate and hence expensive.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a methodof electrical contacting that on the one hand enables the use ofinsulated plug-type elements, for example, in order to satisfy saidsafety regulations, and on the other hand enables plug elements to beproportioned so as to be as small as possible. The method of contactingin accordance with the invention should also enable the manufacture ofas inexpensive as possible plug-type contacts that are notably suitablefor medical disposable articles such as, for example fetal scalpelectrodes. This object is achieved as disclosed in the characterizingpart of the independent claims. Advantageous embodiments are disclosedin the dependent claims.

The invention is based on the idea to design the plug element of aclamping piercing connection that consists of a plug and a socket to besuch that the plug element is enclosed by a molding, prior to theestablishment of an electrical contact, in such a manner that electricalconductors of the plug (at least those that are to be contacted) arecompletely electrically insulated at the contact side. Electricalcontact is then established by the piercing of or cutting into thecorresponding electrical conductors of the plug by contact elements. Themolding may be designed so as to be connected to and integral with theplug conductors or as separate parts, and is preferably essentiallycomplementary to a corresponding recess in the socket in which the plugis to be inserted for the purpose of contacting. Depending on therelevant design, the plug can be introduced into the socket in thepulling direction of the plug conductors, in the direction perpendicularthereto or at an arbitrary angle; pull-out forces for separating theconnection and/or for pulling out the cables can be defined anddetermined by suitable design.

According to the known clamping piercing connections (see notably thecited EP-A-131705 or WO 98/29031), usually only the cables that areinsulated by way of the cable insulation are pierced by appropriateknives and the end of the electrical conductors at the contact side,which is usually only cut off, can thus give rise to undesirableelectrical contacts. In contrast therewith, however, the molding inaccordance with the invention also provides electrical insulation forthe end of the electrical conductors at the contact side, thus enablingundesirable electrical contacts to be avoided.

Because of the essentially complementary design of the molding and thecorresponding socket recess, moreover, the clamping piercing operationcan be specified and concretized in defined insertion positions.Furthermore, suitable codes and/or locking mechanisms can be used inconformity with the relevant application.

The solution in accordance with the invention is particularly suitableto enable the safety contacting necessary for fetal scalp electrodes.However, the solution in accordance with the invention is not restrictedto medical applications in general or to fetal scalp electrodes inparticular, but is suitable for all disengageable plug-type connectionswhere only a small number of insertion and withdrawal cycles is requiredat the plug side. This concerns notably disposable articles or otherapplications where it is necessary to establish a disengageable contactwhich, however, as a rule is closed or opened only once or a few times.

When the solution in accordance with the invention is used, notably inthe case of fetal scalp electrodes, it is ensured that the safetyregulations can be met at low costs. Moreover, the electrical connectionoperation is significantly simplified for the user. Because the usernormally wears protective gloves and such gloves are moist because ofthe vaginal introduction of the fetal scalp electrode, it is not easy tocontrol the customarily used spring jaws and the insertion of the baredwires. This situation is significantly improved by means of a plug-typeconnection in accordance with the invention, because the user canreliably control the plug with one hand only.

Depending on the relevant field of application, the solution inaccordance with the invention enables low-cost manufacture of the plugcontacts that are to be used for small numbers of insertion andwithdrawal cycles. The invention notably enables very inexpensivemanufacture of only a part of the plug-type connection, that is,preferably the insulated plug element. The second part of the plug-typeconnection can then be manufactured at costs that correspond to those ofthe solutions used at present (for example, the costs of tinning thebared wires correspond to the costs of molding a plug in accordance withthe invention around the cable). This means that the advantage of thebasic idea of the solution in accordance with the invention may residenotably in the costs of such plug-type connections where, for example,the costs of the plug should be low and the plug is required for a smallnumber of insertion and withdrawal cycles only. The invention is thusparticularly suitable for disposable articles of the kind frequentlyused for reasons of hygiene in the medical field.

A preferred embodiment of a plug-type connection in accordance with theinvention is provided on the one side (at the cable side) with a plugelement that is arranged on a cable (preferably not bared) and ispreferably molded on the cable while using a synthetic material, and onthe other side (the side to be contacted) with a socket element forreceiving the plug element. A suitable bond can be realized between theplug element and the cable insulation notably when the same syntheticmaterial is used for the plug element and for the cable insulation. Theplug element at the side of the cable is formed in such a manner that itcan be preferably inserted into the opening of the socket element so asto be locked against rotation. During the insertion operation a piercingcontact member that projects into an open space of the socket elementpierces the cable conductor through the insulation and hence establishesan electrical connection between a contact element of the socket elementand the cable conductor. Similarly, in the case of a plurality of cableconductors a plurality of piercing contact members may be provided, eachof said members establishing a respective electrical connection betweena corresponding contact element of the socket element and the relevantcable conductor.

The socket element in a preferred embodiment is formed as a removable orexchangeable element so as to enable a fast exchange of the socket, forexample, in the case of deterioration of the piercing intensity or forthe purpose of cleaning or sterilization of the socket element. Inconformity with the relevant application, the socket element may also beconstructed as a disposable product.

The socket element in another embodiment can be connected in a plug-typefashion to a connection element, for example, to a measuring apparatusor a leg plate (in the case of the fetal scalp electrode) so as toensure a fast and simple exchange. A possibly specified pull-out forcecan then be realized by way of an appropriate design and/orproportioning of this plug-type connection; the socket element thenbecomes disengaged from the connection element under the influence ofpulling. This may be necessary or desirable notably in the case ofmedical applications such as the fetal scalp electrode.

The plug is preferably designed in such a manner that it still has anelectrically insulating effect even after execution of a number ofpiercing clamping operations, be it in some cases to a limited extentonly. This effect can be achieved, for example, by way of a suitablechoice of the materials and/or dimensions of the cable insulation and/orthe molding, so that, for example, the cable insulation and/or themolding return to their initial position (prior to the establishment ofthe piercing clamping connection) to a given degree after thedisengaging of the clamping piercing connection. Furthermore, the riskof undesirable electrical contacts after the disengaging of the piercingclamping connection can be mitigated by providing suitable air gaps.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail hereinafter with reference tothe drawings in which corresponding references relate to functionallyidentical or similar characteristics.

FIG. 1 shows a preferred embodiment of an electrical plug-typeconnection 10 in accordance with the invention,

FIG. 2 shows more detailed views of the plug element 20 that is shown inFIG. 1,

FIGS. 3A and 3B are more detailed views of the socket 30 that is shownin FIG. 1,

FIGS. 4A and 4B show alternative embodiments of piercing elements 50,

FIG. 5 shows a suitable design of a piercing element 50,

FIG. 6 shows an embodiment of the socket element 30, and

FIGS. 7A to 7C illustrate a further embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred embodiment of an electrical plug-typeconnection 10 in accordance with the invention. A plug element 20 (alsoreferred to merely as plug hereinafter) is inserted partly into a socketelement 30 (also referred to hereinafter merely as socket) that is shownin a cut-away view. The shapes of the plug 20 and the socket 30 areadapted to one another; the terms plug and socket in this context haveto be understood in such a manner that the plug element can beintroduced (or plugged) into a socket channel 35 of the socket element.A contact element 40A that is connected to the socket 30 supports, atits side that faces the plug element 20, a piercing (contact) element50A that is only partly visible in FIG. 1. The piercing element 50Aserves to establish, in the state of contact, an electrical contactbetween the contact 40A (preferably to be fed out) of the socket 30 andat least one corresponding electrical conductor of the plug 20.

In the embodiment that is shown in FIG. 1 the plug 20 comprises twocables (or wires) 60A and 60B, each of which contains sheathed and henceinsulated electrical conductors (see 63 in FIG. 2). The piercing element50A of the contact 40A serves to establish an electrical contact withthe conductor 60A and a further contact 40B with a correspondingpiercing element 50B (not visible in the representation chosen forFIG. 1) is intended to contact the conductor 60B.

The plug element 20 is preferably formed by molding around the insulatedcables 60, for example, while using a synthetic material; this enableseconomical manufacture of the plug element 20. Instead of the twoinsulated wires 60A and 60B that are shown in FIG. 1, one or more wires60 can be used in conformity with the relevant application.

FIG. 2 shows more detailed views of the plug element 20 that is shown inFIG. 1. The external shape of the plug element 20 is essentiallycomplementary to the internal shape of the socket 30 so as to ensureinsertion of the plug 20 and the socket 30 one into the other.

The plug element 20 of the preferred embodiment that is shown in theFIGS. 1 and 2 preferably has an external shape that is suitable to lockthe position of the plug element 20 relative to the socket element 30and to preclude undesirable rotation. In the case of a plurality ofcables 60, for example, it can thus be ensured that the individualcables 60 are contacted with the correct polarity or that thecorresponding contacts 40 are associated with the respective individualcables 60. In the example that is shown in the FIGS. 1 and 2 the endface 70 of the plug element 20 that faces the socket 30 is shaped in theform of two letters F that are turned upside down and mirrored relativeto one another or, in other words, as a letter T that stands on its headand is provided with a central stroke that extends parallel to thehorizontal stroke of its head. A resultant head section or strip 75 thatis not situated axially symmetrically (and above the upper horizontalstroke in FIG. 2) relative to a corresponding central horizontal H (inthe insertion direction) thus ensures that the plug 20 is inserted intothe socket 30 with the correct orientation.

Appropriate shaping of the plug element 20 (notably in conformity withthe end face 70) also enables codes to be realized for different typesof plug so that, for example, undesirable connection to an inappropriatesocket 30 is prevented.

For the case where the plug element 20 need not be locked againstrotation, the plug element 20, and notably the end face 70, can also beaxially or point symmetrically configured, so that the contactingbetween the plug element and the socket 30 can take place at a pluralityof angles of rotation, for example, of each time 180°. In that case, forexample, an H-shape (for example, resting on its side as shown in FIG.2) or the like would be suitable.

The suitably realized design of the plug element 20 (preferably byenrobing or molding around the cables 60) includes at the plug side theinsulated cables 60, fixes the position thereof and provides support. Atthe side of the plug element 20 at which the piercing contact element 50penetrates the relevant wire 60 there is preferably provided a recess orcut-out 80 that serves to prevent the knife or knives 50 from beingunnecessarily burdened prior to the actual contacting.

In order to ensure adequate insulation of the cable ends of the cables60 in the plug direction, these cable ends preferably are not fed as faras the end face 70, but only as far as a position that is situated at aselectable distance therefrom. In order to enhance the insulationfurther, in a preferred embodiment a thin layer 90 of preferably asynthetic material is provided between the end of the relevant cable 60and said cut-out 80.

As is shown in the lower part of FIG. 2, the cables 60 are preferablycomposed of a respective (electrical) conductor 63 and an insulation 65that envelops the conductor 63. The conductor 63 may be a singleconductor or may consist of a plurality of individual conductor fibersor litzwires. However, the invention is not limited to the contacting ofcables of the kind that is shown in FIG. 2; arbitrary other cables canalso be used. Notably the plug element 30 need not adjoin the insulation65, but may rest also directly against the conductor 63 so that use canalso be made, for example, of cables wherefrom the insulation 65 hasbeen removed at the plug side.

The FIGS. 3A and 3B are more detailed representations of the socket 30that is shown in FIG. 1; FIG. 3A is a perspective view of the socket 30and FIG. 3B is a cross-sectional view, that is, a view taken at the areaA—A and in the viewing direction indicated by the arrow A. The contacts40A and 40B are provided at opposite sides of the socket channel 35 andthe piercing elements 50A and 50B both project into the socket channel35.

The shape of the socket channel 35 corresponds essentially to the shapeof the plug 20 so as to ensure easy insertion of one into the other. Theshape of the socket channel 35 should also be aimed, if desired, atachieving possible locking against rotation and/or at encoding of theplug 20 and, therefore, is provided with appropriate elements forlocking against rotation and/or for decoding. In the embodiment that isshown in the FIGS. 3A and 3B the socket channel 35 is provided, incorrespondence with the shape of the plug 20 that is shown in FIG. 2,with a cut-out 37 that is complementary to the strip 75.

In the FIGS. 3A and 3B the end of the contacts 40 that is remote fromthe piercing elements 50 is fed out of the housing of the socket 30 forthe purpose of external contacting. However, arbitrary other ways offeeding out of the same contacts 40 from the socket 30 are feasible inconformity with the relevant application. For example, the contacts 40can be fed through in the socket 30 in the direction of the cable axiswithin the socket 30 and be fed out from a side of the socket 30 thatopposes the side of the socket channel 35 where the plug insertionopening is situated.

Contacting is realized by inserting (see FIG. 1) the plug 20 of FIG. 2into the socket element 30 (see FIG. 3B). The piercing (contact)elements 50 are preferably constructed as knives 50 and are arranged insuch a manner that during the insertion operation they first slide intothe cut-out or slit 80 (see FIG. 2) of the plug 20, after which theypenetrate to a given depth (for reasons of safety so as to ensureprotection against touching) into the insulated cable 60 so as toestablish (electrical) contact.

The FIGS. 4A and 4B show alternative embodiments of piercing elements 50for the contacting of cables with a plurality of individual cables 60 i(where i=A, B, . . . ). In FIG. 4A the cables are arranged parallel toone another in a row. In conformity therewith the socket 30 is providedwith a plurality of piercing contact elements 50 i that are concatenatedin a row. In FIG. 4B, however, the plug 20 comprises two mutuallyparallel rows of cables 60 i and, in conformity therewith, the socket 30comprises a respective row of piercing contact elements 50 i above andbelow the cable rows 60 i.

In a preferred embodiment the same material, preferably a syntheticmaterial, as used for the plug element 20 is used for the insulation ofthe cables 60 i; when a synthetic material is used, the plug element 20is preferably molded around the cables 60 i while using this syntheticmaterial. A very good bond can be ensured between the relevant materialswhen the materials for the sheathing/insulation of the cables 60 i andof the plug element 20 are suitably chosen and preferably the samematerials are used for these elements.

The piercing contact elements or knives 50 i in a preferred embodimentare made of a material that is very hard and non-corrosive and ensures asuitable contact. Furthermore, the contact knives 50 i are shaped insuch a manner that they remain sharp as long as possible, thus ensuringthat an adequate number of insertion and withdrawal cycles can takeplace.

The presence of the recesses 80 and the associated exact, sufficientlylong guiding of the plug element 20 in the socket channel 35 of thesocket element 30 ensure that no transverse forces are exerted on thepiercing elements 50 i of the contacts 40 i, so that fracturing of thepiercing elements 50 i can be avoided. For the piercing elements 50 ithemselves a distinction must be made between the cutting part and thepart that establishes the contact. The cutting part should be as long aspossible so as to ensure that it always comprises a sharp section,whereas the part that establishes the contact should extend as slantedas possible, for example at an angle of less than 45°, relative to anylitzwires present in the cables 60 i, thus avoiding the necessity ofsplitting of all fibers (or litzwires) at the same time.

FIG. 5 shows a suitable design of a piercing element 50. The piercingelement comprises a first section that extends preferably at an angle offrom approximately 40 to 50° (preferably 45°) and serves to contact theconductor 63 of the cable 60. The first section 150 is adjoined by asecond section 160 which extends preferably at an angle of fromapproximately 10 to 30° (preferably 22°) and serves to pierce theinsulation 65 and a small part of the conductors 63. Experiments havedemonstrated that 600 insertion and withdrawal cycles are easilypossible when the piercing element is formed in this manner.

FIG. 6 shows a plan view and side elevations of a preferred embodimentof the socket element that enables the plug 20 to be detached from thesocket element 30 when it is pulled in the opposite direction. Thissolution also enables easy replacement of the socket element 30, forexample in the case of a deteriorating piercing intensity or for thepurpose to cleaning or sterilizing the socket element 30. A member 300that is made of a synthetic material and supports the socket 30 inaccordance with the invention on one side is snapped onto a support 310(such as, for example a standard ECG adhesive electrode) by means of asnap fastener 320. In the case of the standard ECG adhesive electrode310, it forms in conjunction with the member 300, for example, a passiveleg plate for attachment to the leg of the patient. Preferably, on itsother side the member 300 is provided with a further contact connection330, for example a socket in conformity with U.S. Pat. No. 5,615,674.

When the element 20 and the socket 30 are joined and a pulling force isexerted, for example, on the cable 60 (not shown in FIG. 6), the member300 of a synthetic material is rotated in the pulling direction aroundthe snap fastener 320. Consequently, the pulling force is always appliedin the pull-out direction of the plug 20, thus enabling easy opening ofthe plug-type connection.

The plug 20 is preferably retained in the socket 30 by the frictionalforces that are produced by the piercing operation. However, in additionto or instead of this clamping connection there may also be provided adifferent retaining system, for example, by locking and/or fastening(for example, by way of trunnions or pins).

A preferred embodiment of a contacting system in accordance with theinvention will be described in detail hereinafter, by way of example,for the contacting of a fetal scalp electrode. Reference is made inparticular to the FIGS. 1 to 3 and 5, said Figures, however, not beinglimited to the application involving the fetal scalp electrode.

The plug element 20 (being the less expensive element) is provided withthe cut-outs 80 for the piercing elements 50 at the right and the leftin the representation of FIG. 2, said piercing elements being shown onthe side of the socket in the FIG. 3. At the area of the cut-outs 80 thepiercing elements 50 are free and do not engage the plug 20. When theplug 20 is inserted further into the socket 30 (beyond the area of thecut-outs 80), the preferably very short insulation layer 90 is cutthrough, the conductors 63 of the cables 60 that are provided with theinsulation 65 are pierced and the contact with the copper wires of theconductor 63 is established when the plug element 20 is insertedfurther.

In the upper region of the plug 20 there is provided the strip 75 and inthe upper region of the socket channel 35 there is provided the cut-out37 that is complementary to said strip 75; these elements thus serve toprovide locking against rotation and to improve the guiding between thesocket 30 and the plug 20, it thus being ensured that the plug can beinserted into the socket 30 in one orientation only.

A stop 200 for the plug 20 as shown in the FIGS. 1 and 2 is provided soas to stop the insertion operation. The stop 200 of the plug 20 thenabuts against the front face of the socket 30 that faces the plug. Thisstop 20 makes sense notably in the case of the fetal application,because in the case of contamination of the socket channel 35, thecontamination can be pushed into the rear area of the socket channel 35wherefrom it can be discharged via an opening 210 as shown in FIG. 1.Such discharging would not be ensured in the case of abutment againstthe end face of the socket channel 35.

In order to form the plug element 20, the cables 60A and 60B as shown inFIG. 1 are arranged in a suitable tool and are kept in position at theleft and the right. Subsequently, an injection molding operation isperformed while using a synthetic material, thus forming a connectionbetween the member of synthetic material and the insulation 65 of thecables 60. The plug 20 thus becomes mechanically stable so that it canbe readily inserted into the socket 30. A cable sleeve or protectionagainst kinking may also be provided, but is not necessary for theapplication involving a fetal scalp electrode, because the plug 20required for this purpose is preferably very small and ductile.

The socket 30 that is provided for the contacting of the plug element 20with the fetal scalp electrode is constructed in conformity with theFIGS. 3A and 3B, but may also have a different construction. Thepiercing elements 50 that are rigidly connected to the contacts 40 arepreferably molded so as to be fixed in the correct position in thesocket 30. The piercing elements 50 themselves preferably have the shapethat is shown in FIG. 5.

The socket 30 itself is preferably snapped, together with a standardfetal socket 330 in conformity with U.S. Pat. No. 5,615,674 in a member300 of a synthetic material, onto a standard ECG adhesive electrode 310by means of a snap fastener 320. The standard ECG adhesive electrode 320constitutes, in conjunction with the member 300 of a synthetic material,a passive leg plate for attachment to the leg of the patient.

The FIGS. 7A to 7C show a further embodiment of the invention. Whereasthe contacting operation in the clamping/plug-type connection that isshown in FIG. 1 takes place essentially in the direction of the cableaxis, the contacting operation in the clamping/plug-type connection thatis shown in FIG. 7 takes place essentially in the directionperpendicular to the cable axis.

In the 3-dimensional representation of FIG. 7A the plug element 20 isinserted into the socket channel 35 of the socket element 30 in thedirection of the arrow. In the contacting state piercing elements 50establish an electrical contact between contacts 40 of the socket 30that are fed out via a cable and the corresponding electrical conductors60 of the plug 20. The plug 20 and the socket 30 in the embodiment thatis shown in the FIG. 7 both comprise two insulated cables.

Because of the essentially complementary design of the plug 20 and thesocket channel 35, the electrical contacts of the plug 20 and the socket30 are already rigidly related to one another, so that in the case of aplurality of cables to be contacted there are only two possiblecombinations, that is, in conformity with the direction of insertionthat is shown in the FIGS. 1 and 7A or with the plug 20 rotated through180° around the cable axis. In conformity with the foregoing, thesepossible combinations can be limited to one permissible combination byappropriate encoding or by taking other suitable steps.

In FIG. 7A such a limitation of the possible combinations is preferablyrealized by way of a nose or projection 700 in the plug element 20; thisprojection 700 co-operates, when introduced from the correct side (inFIG. 7A the plug 20 should be rotated to 180° for this purpose), with acorresponding cut-out or recess (not shown in FIG. 7A) in the socketchannel 35. Instead of such encoding, or in combination therewith, theprojection 700 may also be constructed so as to be resilient, with theresult that it can co-operate with a corresponding recess 710 in thesocket channel 35 and engages, in the case of a correct direction ofinsertion, in the recess 710 as from a given, selectable feed-in depth,for example, in the sense of a snap connection. If no insertion code isprovided, the projection 700 may be configured so as to be so elasticthat both insertion directions are permitted. In this case locking takesplace in the first insertion direction (when the projection 700 and therecess 710 are appropriately brought together), thus possibly increasingthe safety, whereas the second insertion direction (without bringingtogether the projection 700 and the recess 710) is also permitted, be itwithout locking.

The plug 20 and the socket 30 are joined in the direction of the arrowin FIG. 7A. In order to establish the electrical contacts, the plug 20is then pressed against the piercing elements or knives 50 that arepresent in the socket channel 35. In the embodiment that is shown inFIG. 7A each time two knives 50 are provided for each cable 60, saidknives being applied at different positions in the cable direction.Joining can be realized simply by pressing by hand or by means of asuitable device such as a lever mechanism or the like. Furthermore,after successful joining of the plug 20 and the socket 30, theconnection can be protected against the penetration of contaminationsand/or undesirable opening by way of a suitable cover or a lock. Thecover/lock can also be given a disconnect/eject functionality so thatseparation of the plug 20 and the socket 30 is mechanically assisted.

FIG. 7B is an exploded view of a preferred embodiment of the plug 20that is shown in FIG. 7A. The plug 20 is in this case composed of anupper section 750 and a lower section 760. For the assembly of the plug20 the two (insulated) cables 60A and 60B (analogously, only one or morethan two cables could be involved) are inserted into correspondinglydesigned cable ducts 770A and 770B in either the upper section 750 orthe lower section 760, which section is subsequently combined with thecorresponding counter part of the plug 20 (also provided withcorresponding cable ducts 770A and 770B), the upper section 750 and thelower section 760 thus fixing the cables 60A and 60B. The pull-out forcethat is required for pulling out the cables 60 (against the direction ofthe arrow) can be adjusted by appropriate proportioning of the fitbetween the upper section 750 and the lower section 760 (notably of thediameter of the cable ducts 770A and 770B). Similarly, a non-detachableconnection or a more or less readily detachable connection can berealized between the upper section 750 and the lower section 760 byappropriate shaping and design of the upper section 750 and the lowersection 760, so that after assembly the plug 20 is configured as adisposable product or as a possibly re-usable product.

FIG. 7C shows a special embodiment of the lower section 760 that isshown in FIG. 7B, be it rotated through 180° and already connected tothe cables 60 and to the upper section 750. The lower section 760 isprovided with at least one cut-out 780 for each cable 60 at the area ofthe cable duct 770, so that the knives 50 can directly pierce the cableinsulation and need not first cut through the plug 20. The knives 50 arethus spared. Moreover, the plug 20 can then also be constructed so as tohave thicker walls and/or that it can be punched from a harder material.

As is shown in FIG. 7A, the socket 30 and the plug 20 can both beconstructed in such a manner that they are situated at the cable ends ofthe cables 40 and 60.

What is claimed is:
 1. A first contact element for establishingelectrical contact with a second contact element, wherein the secondcontact element defines a contact channel and includes a contactingmember projecting into the contact channel, the first contact elementcomprising: an electrical conductor having a contacting side; and amolding enclosing at least the contacting side of the electricalconductor, said first contact element being shaped such that thecontacting side of the electrical conductor is insertable into thecontact channel of the second contact clement to an inserted positionsuch that the electrical conductor is pierceable by the contactingmember in the second contact element when the first contact element isinserted to the inserted position, the molding having a cut-out area inwhich the contact element of the second contact element is receivableduring a partial insertion of the first contact element such that theelectrical conductor is not pierceable during the partial insertion ofthe first contact element, the molding further having a thin layer ofmaterial, between the end of the electrical conductor at the contactside and the cut-out area.
 2. A second contact element for establishingelectrical contact with a first contact element, the first contactelement having an electrical conductor that is completely electricallyinsulated by a molding in a portion of the first contact element, thesecond contact element comprising: a socket defining a contact channelshaped for receiving the first contact element along an insertiondirection; and a contacting member projecting into the contactingchannel for piercing the electrical conductor disposed in the firstcontact element when the first contact element is received in thecontact channel to establish electrical contact between the contactingmember and the electrical conductor, the contacting member comprising afirst section extending at an angle of 40 to 50 degrees relative to theinsertion direction and a second section extending at an angle of 10 to30 degrees relative to the insertion, wherein the second section isarranged to pierce the molding and the first section is arranged to makeelectrical contact with the electrical conductor of the first contactelement when the first contact element is received in the second contactelement.
 3. A second contact element for establishing electrical contactwith a first contact element, the first contact element having aconductor that is completely electrically insulated by a molding in aportion of the first contact element, which is being received by thesecond contact element, the second contact element comprising: a socketdefining a contact channel for receiving the first contact element; acontacting member projecting into the contacting channel for piercingthe electrical conductor disposed in the first contact element when thefirst contact element is received in the contact channel to establishelectrical contact between the contacting member and the electricalconductor; and said socket further defining a passage disposed betweenan exterior area surrounding the second contact element and the contactchannel for the discharge of material collected in the contact channel,the passage being disposed in a face distal from an opening of thecontact channel where the first contact element is received.
 4. A firstcontact element for establishing an electrical contact with a secondcontact element, the second contact element including a contactingmember and a contacting channel into which the contacting memberprojects, the first contact element comprising: a carrier comprising anelectrically insulating molding and having a central axis, the carrierbeing removably engageable in the contacting channel of the secondcontact element to an insertion position so that the first contactelement is multiply engageable and disengageable with the second contactelement; and a conductor terminated in the carrier and comprising areceiving section carried by the carrier, the receiving section beingreceivable with the carrier in the contact channel of the second contactelement, and the molding being piercable by the contacting member whenthe carrier is engaged to the inserted position so that electricalcontact is establishable between the contacting member and theconductor, the receiving section being completely electrically insulatedby the molding to avoid electrical contact before being first receivedwith the carrier in the second contact element and being substantiallyelectrically insulated when disengaged after being received.
 5. Thefirst contact element of claim 4, wherein said carrier defines a guideslit formed so that the contacting member is guidable in the guide slit,said guide slit being arranged to be insertable in the second contactelement ahead of the conductor.
 6. The first contact element of claim 5,the wherein the molding includes a wall disposed between the guide slitand the conductor relative to the longitudinal direction of the carrier.7. The first contact element of claim 4, wherein the carrier comprises across-section comprising a shape so as prevent rotation in the secondcontact element while engaged in the second contact element.
 8. Thefirst contact element of claim 7, wherein the cross-section comprises anasymmetrical shape wherein the shape is asymmetrical relative to thecentral axis of the carrier, the asymmetrical shape for one ofpreventing rotation in the second contact element while engaged in thesecond contact element and providing a detectable code.
 9. The firstcontact element of claim 4, wherein the carrier comprises an abutmenttransverse to the central axis of the carrier so as to define a firstand a second longitudinal portion of the carrier, wherein only the firstlongitudinal portion is receivable in the second contact element. 10.The first contact element of claim 4, wherein the carrier comprises across-section substantially complementary to a receiving space of thesecond contact element.
 11. The electrical contact device of claim 4,wherein the conductor comprises an electrical insulation and the moldingencloses the electrical insulation.
 12. The first contact element ofclaim 11, the electrical insulation and the molding are integrallyformed by injection molding with a synthetic material.
 13. The firstcontact element of claim 4, wherein the conductor comprises anelectrical insulation and the molding is secured to the electricalinsulation by one of a clamping, crimping, and snapping connection. 14.The first contact element of claim 13, wherein the molding comprises afirst and a second part surrounding the electrical insulation of theconductor.
 15. The first contact element of claim 4, wherein the moldingcomprises a synthetic material for completely electrically insulatingthe conductor before being received in the with the carrier in thesecond element.
 16. The first contact element of claim 4 furthercomprising a plurality of conductors, each conductor terminated in thecarrier and comprising a receiving section carried by the carrier, eachreceiving section being receivable in the second contacting element withthe carrier and pierceable by a respective contacting member disposed inthe second contact element to establish electrical contact with thesecond electrical contact element, the respective receiving sectionsbeing completely electrically insulated by the molding to avoidelectrical contact before being first received with the carrier in thesecond contact element and being substantially electrically insulatedwhen disengaged after being received.
 17. The first contact element ofclaim 4, wherein the conductor comprises an electrical insulation andthe molding comprises a cut-out arranged over the electrical insulationso that the electrical insulation is pierceable by the contacting memberwhen the carrier is engaged to the insertion position.
 18. A secondcontact element for establishing an electrical contact with a firstcontact element, the first contact element carrying a conductor that iscompletely electrically insulated by a molding in a portion of the firstcontact element which is being received by the second contact element,the second contact element comprising: a socket defining a contactchannel for releasably receiving the first contact element along alongitudinal axis, the contact channel comprising a shape that preventsrotation of the first contact element with respect to the second contactelement and receives the first contact element in only one direction;and a contacting member extendable in the contacting channel forpiercing the molding to make electrical contact with the conductor whenthe first contact element is received in the contact channel, the socketbeing multiply engageable and disengageable with the first contactelement.
 19. The second contact element of 18, wherein the contactingmember comprises a first section extending at an angle of 40 to 50degrees relative to the longitudinal axis and a second section extendingat an angle of 10 to 30 degrees relative to the longitudinal axis,wherein the second section is arranged to pierce the molding and thefirst section is arranged to make electrical contact with the electricalconductor of the first contact element when the first contact element isreceived in the second contact element.
 20. The second contact elementof 18, further defining a passage for discharging effluent collected inthe contact channel, the passage providing communication between anexterior of the second contact element and the contact channel, thepassage being disposed in a face of the contact channel distal from anopening of the contact channel in which the first contact element isreceivable.
 21. The second contact element of 18, further comprisingmeans for disengageably coupling to a further device to make the secondcontact element interchangeable.
 22. The second contact element of 21,where the means for disengageably coupling comprises plug-typeconnector.
 23. The second contact element of 18, wherein said contactingmember and contact channel are arranged for creating a frictional forcefor retaining the first contact member when the first contact member isreceived in the contact channel.
 24. A fetal scalp electrode,comprising: a first contact element including a carrier comprising anelectrically insulating molding and a conductor terminated in thecarrier and comprising a receiving section carried by the carrier; and asecond contact element including a contact channel for releasablyreceiving the carrier including at least the receiving section of thefirst contact element to an inserted position and a contacting memberextending into the contacting channel, the contacting member arrangedfor piercing the molding of the first contact element to make electricalcontact with the conductor when the first contact member is received inthe inserted portion, wherein the receiving section of the conductor iscompletely electrically insulated by the molding to avoid electricalcontact before being received in the second contact element andsubstantially electrically insulated when disengaged after beingreceived in the second contact member, and wherein the first and secondcontact elements are multiply engagable and disengageable.